Cone penetrometer systems are commonly used for analyzing subterranean materials and conditions and for developing stratigraphic maps. Recently, cone penetrometer systems have been used in addressing underground contamination problems. Through subsurface analysis, sample recovery, and mapping, cone penetrometer systems have been used to determine the existence and nature of underground contamination problems and to evaluate possible solutions.
A cone penetrometer system will typically utilize a long tubing string having a sensing tool, a sampling tool, and/or some other type of tool positioned on the end thereof. The tubing string is preferably driven, without drilling or turning, into the ground using a hydraulic ram. In some applications, the tubing string is driven 300 or more feet into the ground. For convenience, the hydraulic ram is typically included on a cone penetrometer truck.
In conducting a cone penetrometer test, a relatively small diameter tubing string having a cone on the end thereof is typically driven into the ground first. The cone can be equipped with electronic sensors which take seismic readings and measure such parameters as: the frictional forces encountered by the tubing string; pore water pressure; temperature; inclination; and resistivity. This data is processed and interpreted to obtain a complete stratigraphic map of the test site. Once the stratigraphic data is obtained, the small diameter tubing string is typically pulled out of the ground.
Next, a tubing string having a sample retrieving tool positioned on the end thereof is typically driven into the ground. Sample retrieving tools can be used to obtain underground soil and/or water samples from any particular zone of interest.
The soil sampling tool used heretofore is composed generally of: a sample barrel for collecting the sample material; a rod having one end attached to the end of the penetrometer tubing string; and a tapered driving tip attached to the other end of said rod. As the soil sampling tool is driven into the ground, the rod extends through the sample barrel such that the base end of the sample barrel abuts the end of the tubing string and the driving tip projects from, and blocks, the forward end of the sample barrel. The outside diameter of the base of the driving tip is slightly smaller than the inside diameter of the sample barrel so that the driving tip can be retracted from the forward end of the sample barrel to the base of the sample barrel.
When the soil sampling tool reaches a desired underground sampling location, the penetrometer tubing string is pulled from the ground a sufficient distance to retract the driving tip from the forward end of the sample barrel to the base end of the sample barrel. As the tubing string is being pulled from the ground in order to retract the driving tip, the sample barrel is held at a fixed position in the ground by soil which has compacted around the sample barrel as a result of the driving operation. When the driving tip reaches the base end of the sample barrel, the driving tip and rod automatically lock in place so that the rod can be used to push the sample barrel, which is now open to receive the underground material sample, deeper into the formation. As the sample barrel is pushed deeper into the formation, soil is forced into the forward end of the sample barrel. After the sample barrel has been filled with sample material, the sample barrel is pulled from the ground.
The above-described soil sampling tool is designed primarily for use in stratigraphic analysis rather than environmental analysis. Specifically, the tool is designed primarily to allow the recovery and visual classification of underground soil samples.
The above-described soil sampling tool has numerous shortcomings, particularly when used for collecting samples for environmental analysis. For example, the tool's driving tip does not completely seal the forward end of the sample chamber; consequently, material, e.g., water and/or soil, from other formations enters and contaminates the sample chamber as the sampling tool is driven into the ground. Additionally, since the forward end of the sample barrel must remain open after the sample is taken, unconsolidated sample material can simply fall out of the forward end of the sample barrel as the sample barrel is pulled from the ground. Further, the sample barrel does not hold a sufficient quantity of sample material for the performance of a complete environmental analysis. In order to obtain a quantity of sample material sufficient for a complete environmental analysis, the sampling tool must be driven into and withdrawn from the ground numerous times.
Previous attempts to increase the size of the sample barrel have been largely unsuccessful. Substantially increasing the size of the sample barrel greatly increases the amount of stress encountered by the rod member when said rod member is used to drive the sample chamber deeper into the ground. Further, any increase in the length of the sample chamber must be matched by a corresponding increase in the length of the rod member. However, it has been found that any substantial increase in rod member length greatly increases the risk of rod member breakage.
In addition to the above, it has not been possible heretofore to obtain a continuous core sample using a cone penetrometer system. As indicated, any significant increase in sample chamber length must be matched by a corresponding increase in rod member length. Thus, increasing the length of the sample chamber renders the rod member extremely vulnerable to breakage. Consequently, the collection of a continuous core sample from a depth exceeding about 10 feet has heretofore required the use of a drilling system.